Torque converters generally incorporate a mechanical clutch to bypass the hydrodynamic circuit and improve fuel economy. Often, a torsional isolator is incorporated into the torque converter clutch to reduce transmission of torsional vibrations from the engine to the transmission. Isolator performance is improved when its spring rate is reduced. One way to reduce spring rate is to use multiple sets of springs in a series configuration.
Commonly owned U.S. Pat. No. 6,244,401 (granted Jun. 12, 2001 to Maienschein et al. for “FORCE TRANSMITTING APPARATUS”), herein incorporated by reference, discloses a torque converter with a “series turbine damper” having an input portion engaged with a turbine. The damper has a first damper stage and a second damper stage. In FIG. 2, an intermediate part, or floating flange, represents the output member of the first damper stage and, together with a radially extending flange-like part connected to the intermediate part, holds energy storage devices of the second damper stage.
The floating flange has substantial inertia and its location in the torque path between the sets of concentric springs introduces a degree of freedom (flange mode) that results in objectionable drivetrain vibrations in some vehicles. Maienschein incorporates a plate spring to achieve a desired amount of frictional torque to absorb the flange mode energy. Unfortunately, adding friction degrades isolator performance at all frequencies except the flange mode frequency.
Commonly owned U.S. Pat. No. 7,083,029 (granted Aug. 1, 2006 to Seebacher et al. for “POWER TRANSFER APPARATUS WITH FLUID COUPLING”), herein incorporated by reference, discloses a torque converter having a “double damper” with two damper stages, namely a radially inner stage and a radially outer stage. A runner, or turbine, is rigidly connected to a carrier, which is in turn secured to two discs, or cover plates. The cover plates constitute the input member of the radially inner damper stage.
The mass of the turbine increases the secondary inertia—that is, the inertia positioned after the outer damper stage in the torque path—to oppose engine torsional vibrations and reduce vibrations transmitted to the driveline. Also, adding inertia from the turbine to the cover plates, or floating flange, moves the resonance frequency of the floating flange lower, and out of the driving range in some vehicles. Unfortunately, in other vehicles, the resonance frequency remains in the driving range and results in objectionable drivetrain vibrations.
Thus there is a long-felt need for an improved torque converter design whereby a flange mode is reduced without using friction. There is also a long-felt need for an improved torque converter design whereby transmission of engine torsional vibrations is reduced without introducing objectionable drivetrain vibrations.